Structure-Mediated RNA Decay by UPF1 and G3BP1

Integrative omics indicate FMRP sequesters mRNA from translation and deadenylation in human neuronal cells

How fragile X syndrome protein (FMRP) binds mRNAs and regulates mRNA metabolism remains unclear. Our previous work using human neuronal cells focused on mRNAs targeted for nonsense-mediated mRNA decay (NMD), which we showed are generally bound by FMRP and destabilized upon FMRP loss. Here, we identify >400 high-confidence FMRP-bound mRNAs, only ∼35% of which are NMD targets. Integrative transcriptomics together with SILAC-LC-MS/MS reveal that FMRP loss generally results in mRNA destabilization and more protein produced per FMRP target. We use our established RIP-seq technology to show that FMRP footprints are independent of protein-coding potential, target GC-rich and structured sequences, and are densest in 5' UTRs. Regardless of where within an mRNA FMRP binds, we find that FMRP protects mRNAs from deadenylation and directly binds the cytoplasmic poly(A)-binding protein. Our results reveal how FMRP sequesters polyadenylated mRNAs into stabilized and translationally repressed complexes, whose regulation is critical for neurogenesis and synaptic plasticity.

An improved imaging system that corrects MS2-induced RNA destabilization

The MS2 and MS2-coat protein (MS2-MCP) imaging system is widely used to study messenger RNA (mRNA) spatial distribution in living cells. Here, we report that the MS2-MCP system destabilizes some tagged mRNAs by activating the nonsense-mediated mRNA decay pathway. We introduce an improved version, which counteracts this effect by increasing the efficiency of translation termination of the tagged mRNAs. Improved versions were developed for both yeast and mammalian systems.

Integrated Analysis of TME and Hypoxia Identifies a Classifier to Predict Prognosis and Therapeutic Biomarkers in Soft Tissue Sarcomas

Soft tissue sarcoma (STS) is one of the rarest but most aggressive cancer. It is important to note that intratumoral hypoxia and tumor microenvironment (TME) infiltration play a significant role in the growth and therapeutic resistance of STS. The goal of this study was therefore to determine whether linking hypoxia-related parameters to TME cells could provide a more accurate prediction of prognosis and therapeutic response. An analysis of 109 hypoxia-related genes and 64 TME cells was conducted in STS. Hypoxia-TME classifier was constructed based on 6 hypoxia prognostic genes and 8 TME cells. As a result, we evaluated the prognosis, tumor, and immune characteristics, as well as the effectiveness of therapies in Hypoxia-TME-defined subgroups. The Lowplus group showed a better prognosis and therapeutic response than any other subgroup. It is possible to unravel these differences based on immune-related molecules and somatic mutations in tumors. Further validation of Hypoxia-TME was done in an additional cohort of 225 STS patients. Additionally, we identified five key genes through differential analysis and RT-qPCR, namely, ACSM5, WNT7B, CA9, MMP13, and RAC3, which could be targeted for therapy. As a whole, the Hypoxia-TME classifier demonstrated a pretreatment predictive value for prognosis and therapeutic outcome, providing new approaches to therapy strategizing for patients.

The role of noncoding RNAs in cancer lipid metabolism

Research on noncoding ribonucleic acids (ncRNAs) is mostly and broadly focused on microRNAs (miRNAs), cyclic RNAs (circRNAs), and long ncRNAs (lncRNAs), which have been confirmed to play important roles in tumor cell proliferation, invasion, and migration. Specifically, recent studies have shown that ncRNAs contribute to tumorigenesis and tumor development by mediating changes in enzymes related to lipid metabolism. The purpose of this review is to discuss the characterized ncRNAs involved in the lipid metabolism of tumors to highlight ncRNA-mediated lipid metabolism-related enzyme expression in malignant tumors and its importance to tumor development. In this review, we describe the types of ncRNA and the mechanism of tumor lipid metabolism and analyze the important role of ncRNA in tumor lipid metabolism and its future prospects from the perspectives of ncRNA biological function and lipid metabolic enzyme classification. However, several critical issues still need to be resolved. Because ncRNAs can affect tumor processes by regulating lipid metabolism enzymes, in the future, we can study the unique role of ncRNAs from four aspects: disease prevention, detection, diagnosis, and treatment. Therefore, in the future, the development of ncRNA-targeted therapy will become a hot direction and shoulder a major task in the medical field.

Analyses of circRNA Expression throughout the Light-Dark Cycle Reveal a Strong Regulation of Cdr1as, Associated with Light Entrainment in the SCN

Circular RNAs (circRNAs) are a large class of relatively stable RNA molecules that are highly expressed in animal brains. Many circRNAs have been associated with CNS disorders accompanied by an aberrant wake-sleep cycle. However, the regulation of circRNAs in brain homeostasis over daily light-dark (LD) cycles has not been characterized. Here, we aim to quantify the daily expression changes of circRNAs in physiological conditions in healthy adult animals. Using newly generated and public RNA-Seq data, we monitored circRNA expression throughout the 12:12 h LD cycle in various mouse brain regions. We identified that Cdr1as, a conserved circRNA that regulates synaptic transmission, is highly expressed in the suprachiasmatic nucleus (SCN), the master circadian pacemaker. Despite its high stability, Cdr1as has a very dynamic expression in the SCN throughout the LD cycle, as well as a significant regulation in the hippocampus following the entry into the dark phase. Computational integration of different public datasets predicted that Cdr1as is important for regulating light entrainment in the SCN. We hypothesize that the expression changes of Cdr1as in the SCN, particularly during the dark phase, are associated with light-induced phase shifts. Importantly, our work revises the current beliefs about natural circRNA stability and suggests that the time component must be considered when studying circRNA regulation.

Biogenesis and Regulatory Roles of Circular RNAs

Covalently closed, single-stranded circular RNAs can be produced from viral RNA genomes as well as from the processing of cellular housekeeping noncoding RNAs and precursor messenger RNAs. Recent transcriptomic studies have surprisingly uncovered that many protein-coding genes can be subjected to backsplicing, leading to widespread expression of a specific type of circular RNAs (circRNAs) in eukaryotic cells. Here, we discuss experimental strategies used to discover and characterize diverse circRNAs at both the genome and individual gene scales. We further highlight the current understanding of how circRNAs are generated and how the mature transcripts function. Some circRNAs act as noncoding RNAs to impact gene regulation by serving as decoys or competitors for microRNAs and proteins. Others form extensive networks of ribonucleoprotein complexes or encode functional peptides that are translated in response to certain cellular stresses. Overall, circRNAs have emerged as an important class of RNAmolecules in gene expression regulation that impact many physiological processes, including early development, immune responses, neurogenesis, and tumorigenesis.

Global circRNA expression changes predate clinical and histological improvements of psoriasis patients upon secukinumab treatment

Psoriasis is a common chronic inflammatory skin disease accompanied by heterogenous clinical and histological features, including a characteristic keratinocyte hyperproliferation and dermal immunogenic profile. In addition, psoriasis is associated with widespread transcriptomic alterations including changes in microRNA (miRNA) and circular RNA (circRNA) abundance, which constitute non-coding RNA (ncRNA) classes with specific regulatory capacities in diverse physiological and pathological processes. However, the knowledge about the expression dynamics of ncRNA during psoriasis treatment is sparse. To elucidate the dynamics of miRNA and circRNA abundance during secukinumab (anti-IL-17A) treatment, we studied their expression patterns in skin biopsies from 14 patients with severe plaque-type psoriasis before and during an 84-day secukinumab therapy at day 0, 4, 14, 42, and 84 using NanoString nCounter technology. We found a comprehensive downregulation of the majority of investigated circRNAs and specific alterations in the miRNA profile, including an upregulation of miR-203a-3p, miR-93-5p, and miR-378i in lesional compared to non-lesional skin before treatment. During treatment, the circRNAs progressively returned to the expression levels observed in non-lesional skin and already four days after treatment initiation most circRNAs were significantly upregulated. In comparison, for miRNAs, the normalization to baseline during treatment was delayed and limited to a subset of miRNAs. Moreover, we observed a strong correlation between multiple circRNAs, including ciRS-7 and circPTPRA, and the psoriasis area and severity index (PASI). Similar pronounced correlations could, however, not be found for miRNAs. Finally, we did not observe any significant changes in circRNA expression in peripheral blood mononuclear cells during treatment. In conclusion, we uncovered a rapid shift in global circRNA abundance upon anti-IL-17A treatment, which predated clinical and histological improvements, and a strong correlation with PASI, indicating a biomarker potential of individual circRNAs.

Elucidation of TRIM25 ubiquitination targets involved in diverse cellular and antiviral processes

The tripartite motif (TRIM) family of E3 ubiquitin ligases is well known for its roles in antiviral restriction and innate immunity regulation, in addition to many other cellular pathways. In particular, TRIM25-mediated ubiquitination affects both carcinogenesis and antiviral response. While individual substrates have been identified for TRIM25, it remains unclear how it regulates diverse processes. Here we characterized a mutation, R54P, critical for TRIM25 catalytic activity, which we successfully utilized to "trap" substrates. We demonstrated that TRIM25 targets proteins implicated in stress granule formation (G3BP1/2), nonsense-mediated mRNA decay (UPF1), nucleoside synthesis (NME1), and mRNA translation and stability (PABPC4). The R54P mutation abolishes TRIM25 inhibition of alphaviruses independently of the host interferon response, suggesting that this antiviral effect is a direct consequence of ubiquitination. Consistent with that, we observed diminished antiviral activity upon knockdown of several TRIM25-R54P specific interactors including NME1 and PABPC4. Our findings highlight that multiple substrates mediate the cellular and antiviral activities of TRIM25, illustrating the multi-faceted role of this ubiquitination network in modulating diverse biological processes.

Identification of a non-canonical G3BP-binding sequence in a Mayaro virus nsP3 hypervariable domain

Ras-GTPase-activating SH3 domain-binding-proteins 1 (G3BP1) and 2 (G3BP2) are multifunctional RNA-binding proteins involved in stress granule nucleation, previously identified as essential cofactors of Old World alphaviruses. They are recruited to viral replication complexes formed by the Chikungunya virus (CHIKV), Semliki Forest virus (SFV), and Sindbis virus (SINV) via an interaction with a duplicated FGxF motif conserved in the hypervariable domain (HVD) of virus-encoded nsP3. According to mutagenesis studies, this FGxF duplication is strictly required for G3BP binding and optimal viral growth. Contrasting with this scenario, nsP3 encoded by Mayaro virus (MAYV), an arthritogenic virus grouped with Old World alphaviruses, contains a single canonical FGxF sequence. In light of this unusual feature, we questioned MAYV nsP3/G3BPs relationships. We report that G3BP1 and G3BP2 are both required for MAYV growth in human cells and bind nsP3 protein. In infected cells, they are recruited to nsP3-containing cytosolic foci and active replication complexes. Unexpectedly, deletion of the single FGxF sequence in MAYV nsP3 did not abolish these phenotypes. Using mutagenesis and in silico modeling, we identify an upstream FGAP amino acid sequence as an additional MAYV nsP3/G3BP interaction motif required for optimal viral infectivity. These results, therefore, highlight a non-conventional G3BP binding sequence in MAYV nsP3.

Survey of the binding preferences of RNA-binding proteins to RNA editing events

BACKGROUND

Adenosine-to-inosine (A-to-I) editing is an important RNA posttranscriptional process related to a multitude of cellular and molecular activities. However, systematic characterizations of whether and how the events of RNA editing are associated with the binding preferences of RNA sequences to RNA-binding proteins (RBPs) are still lacking.

RESULTS

With the RNA-seq and RBP eCLIP-seq datasets from the ENCODE project, we quantitatively survey the binding preferences of 150 RBPs to RNA editing events, followed by experimental validations. Such analyses of the RBP-associated RNA editing at nucleotide resolution and genome-wide scale shed light on the involvement of RBPs specifically in RNA editing-related processes, such as RNA splicing, RNA secondary structures, RNA decay, and other posttranscriptional processes.

CONCLUSIONS

These results highlight the relevance of RNA editing in the functions of many RBPs and therefore serve as a resource for further characterization of the functional associations between various RNA editing events and RBPs.

Function and Clinical Significance of Circular RNAs in Thyroid Cancer

Thyroid cancer (TC) is the leading cause and mortality of endocrine malignancies worldwide. Tumourigenesis involves multiple molecules including circular RNAs (circRNAs). circRNAs with covalently closed single-stranded structures have been identified as a type of regulatory RNA because of their high stability, abundance, and tissue/developmental stage-specific expression. Accumulating evidence has demonstrated that various circRNAs are aberrantly expressed in thyroid tissues, cells, exosomes, and body fluids in patients with TC. CircRNAs have been identified as either oncogenic or tumour suppressor roles in regulating tumourigenesis, tumour metabolism, metastasis, ferroptosis, and chemoradiation resistance in TC. Importantly, circRNAs exert pivotal effects on TC through various mechanisms, including acting as miRNA sponges or decoys, interacting with RNA-binding proteins, and translating functional peptides. Recent studies have suggested that many different circRNAs are associated with certain clinicopathological features, implying that the altered expression of circRNAs may be characteristic of TC. The purpose of this review is to provide an overview of recent advances on the dysregulation, functions, molecular mechanisms and potential clinical applications of circRNAs in TC. This review also aimes to improve our understanding of the functions of circRNAs in the initiation and progression of cancer, and to discuss the future perspectives on strategies targeting circRNAs in TC.

The G3BP1-UPF1-Associated Long Non-Coding RNA CALA Regulates RNA Turnover in the Cytoplasm

Besides transcription, RNA decay accounts for a large proportion of regulated gene expression and is paramount for cellular functions. Classical RNA surveillance pathways, like nonsense-mediated decay (NMD), are also implicated in the turnover of non-mutant transcripts. Whereas numerous protein factors have been assigned to distinct RNA decay pathways, the contribution of long non-coding RNAs (lncRNAs) to RNA turnover remains unknown. Here we identify the lncRNA CALA as a potent regulator of RNA turnover in endothelial cells. We demonstrate that CALA forms cytoplasmic ribonucleoprotein complexes with G3BP1 and regulates endothelial cell functions. A detailed characterization of these G3BP1-positive complexes by mass spectrometry identifies UPF1 and numerous other NMD factors having cytoplasmic G3BP1-association that is CALA-dependent. Importantly, CALA silencing impairs degradation of NMD target transcripts, establishing CALA as a non-coding regulator of RNA steady-state levels in the endothelium.

Comparison of Selenium-Enriched Lactobacillusparacasei, Selenium-Enriched Yeast, and Selenite for the Alleviation of DSS-Induced Colitis in Mice

Patients with inflammatory bowel disease (IBD) have been found to have decreased immune function. Selenium (Se) is an essential trace element that is beneficial for human health, which has a significant stimulating effect on immune function. We compared the effects of different Se forms on the alleviation of colitis in DSS-induced mice. Moreover, we also aimed to determine whether Se-enriched Lactobacillus paracasei CCFM 1089 could be used as a new organic Se supplement. Different Se supplements (Se-enriched L. paracasei CCFM 1089, Se-enriched yeast and sodium selenite) were given to Se-deficient mice suffering from colitis. Se-enriched L. paracasei CCFM 1089, which is based on selenocysteine (SeCys), had similar effects in terms of reducing oxidative stress and inhibiting pro-inflammatory factors to Se-enriched yeast; however, selenase activity in the Se-enriched L. paracasei CCFM 1089-treated mice was higher than that in other treatment groups. In addition, Se-enriched L. paracasei CCFM 1089 could better protect the intestinal mucosa, which increased the expression of tight junction proteins (ZO-1 and occludin) in mice. Thus Se-enriched L. paracasei CCFM 1089 was shown to alleviate IBD, suggesting that it has potential as a good organic Se supplement.

Comprehensive Profiling Reveals Prognostic and Immunogenic Characteristics of Necroptosis in Soft Tissue Sarcomas

Soft tissue sarcomas (STSs) are heterogeneous malignancies derived from mesenchymal cells. Due to its rarity, heterogeneity, and limited overall response to chemotherapy, STSs represent a therapeutic challenge. Necroptosis is a novel therapeutic strategy for enhancing immunotherapy of cancer. Nevertheless, no research has explored the relationship between necroptosis-related genes (NRGs) and STSs. In this study, differentially expressed NRGs were identified using The Cancer Genome Atlas (TCGA) and The Cancer Genotype-Tissue Expression (GTEx) project. The expression levels of 34 NRGs were significantly different. Several key NRGs were validated using RT-qPCR and our own sequencing data. Patients with STSs were divided into two clusters using consensus cluster analysis, and significant differences were observed in their survival (p=0.002). We found the differentially expressed genes (DEGs) between the two clusters and carried out subsequent analysis. The necroptosis-related gene signatures with 10 key DEGs were identified with a risk score constructed. The prognosis of TCGA-SARC cohort with low necroptosis-related risk score was better (p<0.001). Meanwhile, the low-risk group had a significantly increased immune infiltration. Using the data of GSE17118 and another immunotherapy cohort as external validations, we observed significant survival differences between the two risk groups (p=0.019). The necroptosis-related risk score proved to be an independent prognostic factor, and a nomogram was further established and integrated with other clinical features. Notably, the necroptosis-related gene signature could also act as the prognostic indicator in other malignancies based on pan-cancer analysis. In summary, the study outlines NRGs in STSs and their potential role in prognosis and will be one of the important directions for future research.

Sequestration of TDP-43216-414 Aggregates by Cytoplasmic Expression of the proSAAS Chaperone

As neurons age, protein homeostasis becomes less efficient, resulting in misfolding and aggregation. Chaperone proteins perform vital functions in the maintenance of cellular proteostasis, and chaperone-based therapies that promote sequestration of toxic aggregates may prove useful in blocking the development of neurodegenerative disease. We previously demonstrated that proSAAS, a small secreted neuronal protein, exhibits potent chaperone activity against protein aggregation in vitro and blocks the cytotoxic effects of amyloid and synuclein oligomers in cell culture systems. We now examine whether cytoplasmic expression of proSAAS results in interactions with protein aggregates in this cellular compartment. We report that expression of proSAAS within the cytoplasm generates dense, membraneless 2 μm proSAAS spheres which progressively fuse to form larger spheres, suggesting liquid droplet-like properties. ProSAAS spheres selectively accumulate a C-terminally truncated fluorescently tagged form of TDP-43, initiating its cellular redistribution; these TDP-43-containing spheres also exhibit dynamic fusion. Efficient encapsulation of TDP-43 into proSAAS spheres is driven by its C-terminal prion-like domain; spheres must be formed for sequestration to occur. Three proSAAS sequences, a predicted coiled-coil, a conserved region (residues 158-169), and the positively charged sequence 181-185, are all required for proSAAS to form spheres able to encapsulate TDP-43 aggregates. Substitution of lysines for arginines in the 181-185 sequence results in nuclear translocation of proSAAS and encapsulation of nuclear-localized TDP-43216-414. As a functional output, we demonstrate that proSAAS expression results in cytoprotection against full-length TDP-43 toxicity in yeast. We conclude that proSAAS can act as a functional holdase for TDP-43 via this phase-separation property, representing a cytoprotectant whose unusual biochemical properties can potentially be exploited in the design of therapeutic molecules.

Neuronal Cells Display Distinct Stability Controls of Alternative Polyadenylation mRNA Isoforms, Long Non-Coding RNAs, and Mitochondrial RNAs

RNA stability plays an important role in gene expression. Here, using 3' end sequencing of newly made and pre-existing poly(A)+ RNAs, we compare transcript stability in multiple human cell lines, including HEK293T, HepG2, and SH-SY5Y. We show that while mRNA stability is generally conserved across the cell lines, specific transcripts having a high GC content and possibly more stable secondary RNA structures are relatively more stable in SH-SY5Y cells compared to the other 2 cell lines. These features also differentiate stability levels of alternative polyadenylation (APA) 3'UTR isoforms in a cell type-specific manner. Using differentiation of a neural stem cell line as a model, we show that mRNA stability difference could contribute to gene expression changes in neurogenesis and confirm the neuronal identity of SH-SY5Y cells at both gene expression and APA levels. In addition, compared to transcripts using 3'-most exon cleavage/polyadenylation sites (PASs), those using intronic PASs are generally less stable, especially when the PAS-containing intron is large and has a strong 5' splice site, suggesting that intronic polyadenylation mostly plays a negative role in gene expression. Interestingly, the differential mRNA stability among APA isoforms appears to buffer PAS choice in these cell lines. Moreover, we found that several other poly(A)+ RNA species, including promoter-associated long noncoding RNAs and transcripts encoded by the mitochondrial genome, are more stable in SH-SY5Y cells than the other 2 cell lines, further highlighting distinct RNA metabolism in neuronal cells. Together, our results indicate that distinct RNA stability control in neuronal cells may contribute to the gene expression and APA programs that define their cell identity.

Fuzzy RNA recognition by the Trypanosoma brucei editosome

The assembly of high molecular mass ribonucleoprotein complexes typically relies on the binary interaction of defined RNA sequences or precisely folded RNA motifs with dedicated RNA-binding domains on the protein side. Here we describe a new molecular recognition principle of RNA molecules by a high molecular mass protein complex. By chemically probing the solvent accessibility of mitochondrial pre-mRNAs when bound to the Trypanosoma brucei editosome, we identified multiple similar but non-identical RNA motifs as editosome contact sites. However, by treating the different motifs as mathematical graph objects we demonstrate that they fit a consensus 2D-graph consisting of 4 vertices (V) and 3 edges (E) with a Laplacian eigenvalue of 0.5477 (λ₂). We establish that synthetic 4V(3E)-RNAs are sufficient to compete for the editosomal pre-mRNA binding site and that they inhibit RNA editing in vitro. Furthermore, we demonstrate that only two topological indices are necessary to predict the binding of any RNA motif to the editosome with a high level of confidence. Our analysis corroborates that the editosome has adapted to the structural multiplicity of the mitochondrial mRNA folding space by recognizing a fuzzy continuum of RNA folds that fit a consensus graph descriptor.

The roles of G3BP1 in human diseases (review)

Ras-GTPase-activating protein binding protein 1 (G3BP1) is a multifunctional binding protein involved in a variety of biological functions, including cell proliferation, metastasis, apoptosis, differentiation and RNA metabolism. It has been revealed that G3BP1, as an antiviral factor, can interact with viral proteins and regulate the assembly of stress granules (SGs), which can inhibit viral replication. Furthermore, several viruses have the ability to hijack G3BP1 as a cofactor, recruiting translation initiation factors to promote viral proliferation. However, many functions of G3BP1 are associated with other diseases. In various cancers, G3BP1 is a cancer-promoting factor, which can promote the proliferation, invasion and metastasis of cancer cells. Moreover, compared with normal tissues, G3BP1 expression is higher in tumor tissues, indicating that it can be used as an indicator for cancer diagnosis. In this review, the structure of G3BP1 and the regulation of G3BP1 in multiple dimensions are described. In addition, the effects and potential mechanisms of G3BP1 on various carcinomas, viral infections, nervous system diseases and cardiovascular diseases are elucidated, which may provide a direction for clinical applications of G3BP1 in the future.

The emerging roles of circRNAs in cancer and oncology

Over the past decade, circular RNAs (circRNAs) have emerged as a large class of primarily non-coding RNA molecules, many of which have key roles in cancer development and progression through diverse mechanisms of action. CircRNAs often have tissue-restricted and cancer-specific expression patterns, and accumulating data suggest that these molecules are of potential clinical relevance and utility. In particular, circRNAs have strong potential as diagnostic, prognostic and predictive biomarkers, which is underscored by their detectability in liquid biopsy samples such as in plasma, saliva and urine. However, technical issues in the detection and assessment of circRNAs as well as biological knowledge gaps need to be addressed to move this relatively young field of research forward and bring circRNAs to the forefront of clinical practice. Herein, we review the current knowledge regarding circRNA biogenesis, regulation and functions in cancer as well as their clinical potential as biomarkers, therapeutic agents and drug targets.

Circular RNA in disease: Basic properties and biomedical relevance

Circular RNAs (circRNAs) represent a class of covalently closed RNA molecules with great diversity in molecular features, functions, and regulatory mechanisms. Emerging advances in our understanding of circRNA biogenesis, nuclear export, and stability control have been made very recently. In particular, novel roles of circRNAs in diverse human diseases are increasingly recognized. Various circRNAs have been found to affect many disease-relevant pathways through a diverse array of mechanisms, including forming R-loops, sponging miRNAs or proteins, and translating functional proteins, resulting in different pathological phenotypes. This recent progress calls for a revised view of circRNAs in diseases threatening the lives and health of humans. In this review, we focus on the recently described functional relevance of disease-associated circRNAs as well as the potential of circRNAs in diverse clinical applications. This article is categorized under: RNA in Disease and Development > RNA in Disease Regulatory RNAs/RNAi/Riboswitches > Regulatory RNAs.

Circular RNAs Modulate Cancer Hallmark and Molecular Pathways to Support Cancer Progression and Metastasis

Simple Summary

Circular RNAs (circRNA) are a type of RNA molecule of circular shape that are now being extensively studied due to the important roles they play in different biological processes. In addition, they were also shown to be implicated in disease such as cancer. Cancer is a complex process which is often defined by a combination of specific processes called cancer hallmarks. In this review, we summarize the literature on circRNAs in cancer and classify them as being implicated in specific cancer hallmarks.

Abstract

Circular RNAs (circRNAs) are noncoding products of backsplicing of pre-mRNAs which have been established to possess potent biological functions. Dysregulated circRNA expression has been linked to diseases including different types of cancer. Cancer progression is known to result from the dysregulation of several molecular mechanisms responsible for the maintenance of cellular and tissue homeostasis. The dysregulation of these processes is defined as cancer hallmarks, and the molecular pathways implicated in them are regarded as the targets of therapeutic interference. In this review, we summarize the literature on the investigation of circRNAs implicated in cancer hallmark molecular signaling. First, we present general information on the properties of circRNAs, such as their biogenesis and degradation mechanisms, as well as their basic molecular functions. Subsequently, we summarize the roles of circRNAs in the framework of each cancer hallmark and finally discuss the potential as therapeutic targets.

N6-methyladenosine-dependent modification of circGARS acts as a new player that promotes SLE progression through the NF-κB/A20 axis

Background

Certain circRNAs could be used as biomarkers to determine the risk of development and/or severity of systemic lupus erythematosus, and their new function in the regulation of gene expression has motivated us to investigate their role in SLE

Methods

Experimental methods including qRT-PCR, RNA immunoprecipitation (RIP), pulldown, dual luciferase reporter assay, RNA interference and cell transfection, RNA fluorescence in situ hybridization, western blotting, and mass spectrometry were used to assessed circGARS (hsa_circRNA_0009000) for immune functions and defined mechanisms by which circGARS promotes the progression in SLE.

Results

Our results demonstrated that the levels of circGARS was remarkably upregulated in SLE and correlated with clinicopathological features. CircGARS directly combined with microRNA-19a (miR-19a). Functionally, circGARS downregulated the expression of TNFAIP3 (A20, tumor necrosis factor alpha-induced protein 3) to mediate the activation of immune responses that were regulated by the nuclear factor-κB (NF-κB) pathway as a negative feedback mechanism. In addition, miR-19a regulated A20 (TNFAIP3) degradation by downregulating the expression of YTH N6-methyladenosine RNA-binding protein 2 (YTHDF2).

Conclusions

The circGARS sponges miR-19a to regulate YTHDF2 expression to promote SLE progression through the A20/NF-κB axis and may act as an independent biomarker to help the treatment of SLE patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-022-02732-x.

Circular RNAs exhibit limited evidence for translation, or translation regulation of the mRNA counterpart in terminal hematopoiesis

Each day, about 10¹² erythrocytes and platelets are released into the bloodstream. This substantial output from hematopoietic stem cells is tightly regulated by transcriptional and epigenetic factors. Whether and how circular RNAs (circRNAs) contribute to the differentiation and/or identity of hematopoietic cells is to date not known. We recently reported that erythrocytes and platelets contain the highest levels and numbers of circRNAs among hematopoietic cells. Here, we provide the first detailed analysis of circRNA expression during erythroid and megakaryoid differentiation. CircRNA expression not only significantly increased upon enucleation, but also had limited overlap between progenitor cells and mature cells, suggesting that circRNA expression stems from regulated processes rather than resulting from mere accumulation. To study circRNA function in hematopoiesis, we first compared the expression levels of circRNAs with the translation efficiency of their mRNA counterpart. We found that only one out of 2531 (0.04%) circRNAs associated with mRNA-translation regulation. Furthermore, irrespective of thousands of identified putative open reading frames, deep ribosome-footprinting sequencing, and mass spectrometry analysis provided little evidence for translation of endogenously expressed circRNAs. In conclusion, circRNAs alter their expression profile during terminal hematopoietic differentiation, yet their contribution to regulate cellular processes remains enigmatic.

Translation and emerging functions of non-coding RNAs in inflammation and immunity

Regulatory non‐coding RNAs (ncRNAs) including small non‐coding RNAs (sRNAs), long non‐coding RNAs (lncRNAs), and circular RNAs (circRNAs) have gained considerable attention in the last few years. This is mainly due to their condition‐ and tissue‐specific expression and their various modes of action, which suggests them as promising biomarkers and therapeutic targets. One important mechanism of ncRNAs to regulate gene expression is through translation of short open reading frames (sORFs). These sORFs can be located in lncRNAs, in non‐translated regions of mRNAs where upstream ORFs (uORFs) represent the majority, or in circRNAs. Regulation of their translation can function as a quick way to adapt protein production to changing cellular or environmental cues, and can either depend solely on the initiation and elongation of translation, or on the roles of the produced functional peptides. Due to the experimental challenges to pinpoint translation events and to detect the produced peptides, translational regulation through regulatory RNAs is not well studied yet. In the case of circRNAs, they have only recently started to be recognized as regulatory molecules instead of mere artifacts of RNA biosynthesis. Of the many roles described for regulatory ncRNAs, we will focus here on their regulation during inflammation and in immunity.

Insights into the multifaceted role of circular RNAs: implications for Parkinson's disease pathogenesis and diagnosis

Parkinson's disease (PD) is a complex, age-related, neurodegenerative disease whose etiology, pathology, and clinical manifestations remain incompletely understood. As a result, care focuses primarily on symptoms relief. Circular RNAs (circRNAs) are a large class of mostly noncoding RNAs that accumulate with aging in the brain and are increasingly shown to regulate all aspects of neuronal and glial development and function. They are generated by the spliceosome through the backsplicing of linear RNA. Although their biological role remains largely unknown, they have been shown to regulate transcription and splicing, act as decoys for microRNAs and RNA binding proteins, used as templates for translation, and serve as scaffolding platforms for signaling components. Considering that they are stable, diverse, and detectable in easily accessible biofluids, they are deemed promising biomarkers for diagnosing diseases. CircRNAs are differentially expressed in the brain of patients with PD, and growing evidence suggests that they regulate PD pathogenetic processes. Here, the biogenesis, expression, degradation, and detection of circRNAs, as well as their proposed functions, are reviewed. Thereafter, research linking circRNAs to PD-related processes, including aging, alpha-synuclein dysregulation, neuroinflammation, and oxidative stress is highlighted, followed by recent evidence for their use as prognostic and diagnostic biomarkers for PD.

Loss of Ras GTPase-activating protein SH3 domain-binding protein 1 (G3BP1) inhibits the progression of ovarian cancer in coordination with ubiquitin-specific protease 10 (USP10)

Ovarian cancer (OC) is one of the most lethal gynecological malignancies. However, the molecular mechanisms underlying the development of OC remain unclear. Here, we report that loss of Ras GTPase-activating protein SH3 domain-binding protein 1 (G3BP1) inhibits the progression of OC cells. Analysis of databases and clinical specimens showed that G3BP1 is upregulated in OC. The Kaplan-Meier plot results showed that G3BP1 is highly expressed in OC with a poor clinical outcome. Moreover, loss-of-G3BP1 suppresses the proliferation, migration, and invasion of OC cells. Protein-protein interaction network analysis and immunoprecipitation assay showed that ubiquitin-specific protease 10 (USP10) interacts with G3BP1. We next found that USP10 coordinately promotes tumor progression with G3BP1. Moreover, loss of USP10could restore the G3BP1-induced proliferation, migration, and invasion of OC cells. These data indicate that G3BP1 coordinated with USP10 to facilitate the progression of OC cells, and that G3BP1 may become a treatment target for OC.

Uncovering viral RNA-host cell interactions on a proteome-wide scale

RNA viruses interact with a wide range of cellular RNA-binding proteins (RBPs) during their life cycle. The prevalence of these host-virus interactions has been highlighted by new methods that elucidate the composition of viral ribonucleoproteins (vRNPs). Applied to 11 viruses so far, these approaches have revealed hundreds of cellular RBPs that interact with viral (v)RNA in infected cells. However, consistency across methods is limited, raising questions about methodological considerations when designing and interpreting these studies. Here, we discuss these caveats and, through comparing available vRNA interactomes, describe RBPs that are consistently identified as vRNP components and outline their potential roles in infection. In summary, these novel approaches have uncovered a new universe of host-virus interactions holding great therapeutic potential.

Circ-Hdgfrp3 shuttles along neurites and is trapped in aggregates formed by ALS-associated mutant FUS

CircRNAs belong to a family of RNA molecules which are conserved in evolution, have tissue-specific expression, and are abundant in neuronal cells. Here, we define several features of circ-Hdgfrp3 and describe interesting alterations occurring in motor neurons (MNs) carrying ALS-associated FUS mutations. Through a highly sensitive in situ approach we describe that circ-Hdgfrp3 traffics along neurites, while upon oxidative stress it is retained in the perinuclear region. While in wild-type stressed MNs, circ-Hdgfrp3 localizes in stress granules (SGs), in MNs carrying mutant FUS, a higher proportion of circ-Hdgfrp3 was trapped into cytoplasmic aggregates. Upon stress removal, circ-Hdgfrp3 was easily freed from SGs whereas it was less efficiently released from FUS-aggregates. We found that the human circ-Hdgfrp3 counterpart was also similarly associated to mutant FUS-aggregates in stressed neuronal cells. Overall, the alteration of circ-Hdgfrp3 trafficking adds a further layer of complexity to the role of FUS-aggregates in ALS disease.

Multifunctional RNA-binding proteins influence mRNA abundance and translational efficiency of distinct sets of target genes

RNA-binding proteins (RBPs) can regulate more than a single aspect of RNA metabolism. We searched for such previously undiscovered multifunctionality within a set of 143 RBPs, by defining the predictive value of RBP abundance for the transcription and translation levels of known RBP target genes across 80 human hearts. This led us to newly associate 27 RBPs with cardiac translational regulation in vivo. Of these, 21 impacted both RNA expression and translation, albeit for virtually independent sets of target genes. We highlight a subset of these, including G3BP1, PUM1, UCHL5, and DDX3X, where dual regulation is achieved through differential affinity for target length, by which separate biological processes are controlled. Like the RNA helicase DDX3X, the known splicing factors EFTUD2 and PRPF8—all identified as multifunctional RBPs by our analysis—selectively influence target translation rates depending on 5’ UTR structure. Our analyses identify dozens of RBPs as being multifunctional and pinpoint potential novel regulators of translation, postulating unanticipated complexity of protein-RNA interactions at consecutive stages of gene expression.

The lifecycle of an RNA molecule is controlled by hundreds of proteins that can bind RNA, also known as RNA-binding proteins (RBPs). These proteins recognize landing sites within the RNA and guide the RNA’s transcription from DNA, its processing into a mature messenger RNA, its translation into protein, or its degradation once the RNA is no longer needed. Although we now mechanistically understand how certain RBPs regulate these processes, for many RBP-target interactions the consequences imposed by RNA binding are not well understood. For 143 RBPs with known RNA binding positions, the authors of the current study investigated how RNA molecules responded to fluctuations in the expression levels of these RBPs, across each of 80 human hearts. Using statistical approaches, they could show that many RBPs influenced stages of the RNA lifecycle that they were not known to be involved in. Some RBPs turned out to be true "all-rounders" of RNA metabolism: they controlled the RNA transcript levels of some genes, whereas they influenced the translation rates of others. This unexpected multifunctionality unveiled previously hidden aspects of the everyday RNA-binding protein working life.

RNA circles with minimized immunogenicity as potent PKR inhibitors

Exon back-splicing-generated circular RNAs, as a group, can suppress double-stranded RNA (dsRNA)-activated protein kinase R (PKR) in cells. We have sought to synthesize immunogenicity-free, short dsRNA-containing RNA circles as PKR inhibitors. Here, we report that RNA circles synthesized by permuted self-splicing thymidylate synthase (td) introns from T4 bacteriophage or by Anabaena pre-tRNA group I intron could induce an immune response. Autocatalytic splicing introduces ∼74 nt td or ∼186 nt Anabaena extraneous fragments that can distort the folding status of original circular RNAs or form structures themselves to provoke innate immune responses. In contrast, synthesized RNA circles produced by T4 RNA ligase without extraneous fragments exhibit minimized immunogenicity. Importantly, directly ligated circular RNAs that form short dsRNA regions efficiently suppress PKR activation 10³- to 10⁶-fold higher than reported chemical compounds C16 and 2-AP, highlighting the future use of circular RNAs as potent inhibitors for diseases related to PKR overreaction.

Profiling of Plasma Extracellular Vesicle Transcriptome Reveals That circRNAs Are Prevalent and Differ between Multiple Sclerosis Patients and Healthy Controls

(1) Background: Extracellular vesicles (EVs) are released by most cell types and are implicated in several biological and pathological processes, including multiple sclerosis (MS). Differences in the number and cargo of plasma-derived EVs have been described in MS. In this work, we have characterised the EV RNA cargo of MS patients, with particular attention to circular RNAs (circRNAs), which have attracted increasing attention for their roles in physiology and disease and their biomarker potential. (2) Methods: Plasma-derived EVs were isolated by differential centrifugation (20 patients, 8 controls), and RNA-Sequencing was used to identify differentially expressed linear and circRNAs. (3) Results: We found differences in the RNA type distribution, circRNAs being enriched in EVs vs. leucocytes. We found a number of (corrected p-value < 0.05) circRNA significantly DE between the groups. Nevertheless, highly structured circRNAs are preferentially retained in leukocytes. Differential expression analysis reports significant differences in circRNA and linear RNA expression between MS patients and controls, as well as between different MS types. (4) Conclusions: Plasma derived EV RNA cargo is not a representation of leukocytes’ cytoplasm but a message worth studying. Moreover, our results reveal the interest of circRNAs as part of this message, highlighting the importance of further understanding RNA regulation in MS.

Circular RNAs in physiology and non-immunological diseases

Circular RNAs (circRNAs) are covalently closed single-stranded RNAs. Four subclasses of circRNAs have been identified in animal cells, and they have unique features in their biogenesis, degradation, and transport. CircRNAs have diverse molecular functions in sponging miRNAs, regulating transcription, modulating RNA-binding proteins, and even encoding proteins. Some circRNAs are important regulators of various physiological processes to maintain homeostasis. Dysregulation of circRNAs is associated with human disorders, and individual circRNAs are crucial factors that contribute to major diseases including non-immunological diseases such as cancers, neurological disorders, cardiovascular disease, and metabolic disease. Debates on circRNAs have also been raised in recent years, and further studies would help to resolve these disputes and potentially lead to biomedical applications of circRNAs.

The potential of using blood circular RNA as liquid biopsy biomarker for human diseases

Circular RNA (circRNA) is a novel class of single-stranded RNAs with a closed loop structure. The majority of circRNAs are formed by a back-splicing process in pre-mRNA splicing. Their expression is dynamically regulated and shows spatiotemporal patterns among cell types, tissues and developmental stages. CircRNAs have important biological functions in many physiological processes, and their aberrant expression is implicated in many human diseases. Due to their high stability, circRNAs are becoming promising biomarkers in many human diseases, such as cardiovascular diseases, autoimmune diseases and human cancers. In this review, we focus on the translational potential of using human blood circRNAs as liquid biopsy biomarkers for human diseases. We highlight their abundant expression, essential biological functions and significant correlations to human diseases in various components of peripheral blood, including whole blood, blood cells and extracellular vesicles. In addition, we summarize the current knowledge of blood circRNA biomarkers for disease diagnosis or prognosis.

Circular RNAs in kidney disease and cancer

Circular RNAs (circRNAs) are a class of endogenously expressed regulatory RNAs with a single-stranded circular structure. They are generated by back splicing and their expression can be tightly regulated by RNA binding proteins. Cytoplasmic circRNAs can function as molecular sponges that inhibit microRNA-target interactions and protein function or as templates for the efficient generation of peptides via rolling circle amplification. They can also act as molecular scaffolds that enhance the reaction kinetics of enzyme-substrate interactions. In the nucleus, circRNAs might facilitate chromatin modifications and promote gene expression. CircRNAs are resistant to degradation and can be packaged in extracellular vesicles and transported in the circulation. Initial studies suggest that circRNAs have roles in kidney disease and associated cardiovascular complications. They have been implicated in hypertensive nephropathy, diabetic kidney disease, glomerular disease, acute kidney injury and kidney allograft rejection, as well as in microvascular and macrovascular complications of chronic kidney disease, including atherosclerotic vascular disease. In addition, several circRNAs have been reported to have oncogenic or tumour suppressor roles or to regulate drug resistance in kidney cancer. The available data suggest that circRNAs could be promising diagnostic and/or prognostic biomarkers and potential therapeutic targets for kidney disease, cardiovascular disease and kidney cancer.

G3BP1 binds to guanine quadruplexes in mRNAs to modulate their stabilities

RNA guanine quadruplexes (rG4) assume important roles in post-transcriptional regulations of gene expression, which are often modulated by rG4-binding proteins. Hence, understanding the biological functions of rG4s requires the identification and functional characterizations of rG4-recognition proteins. By employing a bioinformatic approach based on the analysis of overlap between peaks obtained from rG4-seq analysis and those detected in >230 eCLIP-seq datasets for RNA-binding proteins generated from the ENCODE project, we identified a large number of candidate rG4-binding proteins. We showed that one of these proteins, G3BP1, is able to bind directly to rG4 structures with high affinity and selectivity, where the binding entails its C-terminal RGG domain and is further enhanced by its RRM domain. Additionally, our seCLIP-Seq data revealed that pyridostatin, a small-molecule rG4 ligand, could displace G3BP1 from mRNA in cells, with the most pronounced effects being observed for the 3′-untranslated regions (3′-UTR) of mRNAs. Moreover, luciferase reporter assay results showed that G3BP1 positively regulates mRNA stability through its binding with rG4 structures. Together, we identified a number of candidate rG4-binding proteins and validated that G3BP1 can bind directly with rG4 structures and regulate the stabilities of mRNAs.

Dissecting the Role of Circular RNAs in Sarcomas with Emphasis on Osteosarcomas

Circular RNAs (circRNAs) are single-stranded RNAs generated from exons back-splicing from a single pre-mRNA, forming covalently closed loop structures which lack 5'-3'-polarity or polyadenylated tail. Ongoing research depicts that circRNAs play a pivotal role in tumorigenesis, tumor progression, metastatic potential and chemoresistance by regulating transcription, microRNA (miRNA) sponging, RNA-binding protein interactions, alternative splicing and to a lesser degree, protein coding. Sarcomas are rare malignant tumors stemming from mesenchymal cells. Due to their clinically insidious onset, they often present at advanced stage and their treatment may require aggressive chemotherapeutic or surgical options. This review is mainly focused on the regulatory functions of circRNAs on osteosarcoma progression and their potential role as biomarkers, an area which has prompted lately extensive research. The attributed oncogenic role of circRNAs on other mesenchymal tumors such as Kaposi Sarcoma (KS), Rhabdomyosarcoma (RMS) or Gastrointestinal Stromal Tumors (GISTs) is also described. The involvement of circRNAs on sarcoma oncogenesis and relevant emerging diagnostic, prognostic and therapeutic applications are expected to gain more research interest in the future.

Circular RNAs in cell cycle regulation: Mechanisms to clinical significance

Circular RNAs (circRNAs), a type of non‐coding RNA, are single‐stranded circularized molecules characterized by high abundance, evolutionary conservation and cell development‐ and tissue‐specific expression. A large body of studies has found that circRNAs exert a wide variety of functions in diverse biological processes, including cell cycle. The cell cycle is controlled by the coordinated activation and deactivation of cell cycle regulators. CircRNAs exert mutifunctional roles by regulating gene expression via various mechanisms. However, the functional relevance of circRNAs and cell cycle regulation largely remains to be elucidated. Herein, we briefly describe the biogenesis and mechanistic models of circRNAs and summarize their functions and mechanisms in the regulation of critical cell cycle modulators, including cyclins, cyclin‐dependent kinases and cyclin‐dependent kinase inhibitors. Moreover, we highlight the participation of circRNAs in cell cycle‐related signalling pathways and the clinical value of circRNAs as promising biomarkers or therapeutic targets in diseases related to cell cycle disorder.

Crosstalk between N6-methyladenosine modification and circular RNAs: current understanding and future directions

N⁶-methyladenosine (m⁶A) is a prevalent internal modification in eukaryotic RNAs regulated by the so-called "writers", "erasers", and "readers". m⁶A has been demonstrated to exert critical molecular functions in modulating RNA maturation, localization, translation and metabolism, thus playing an essential role in cellular, developmental, and disease processes. Circular RNAs (circRNAs) are a class of non-coding RNAs with covalently closed single-stranded structures generated by back-splicing. CircRNAs also participate in physiological and pathological processes through unique mechanisms. Despite their discovery several years ago, m⁶A and circRNAs has drawn increased research interest due to advances in molecular biology techniques these years. Recently, several scholars have investigated the crosstalk between m⁶A and circRNAs. In this review, we provide an overview of the current knowledge of m⁶A and circRNAs, as well as summarize the crosstalk between these molecules based on existing research. In addition, we present some suggestions for future research perspectives.

Phase separation of a plant virus movement protein and cellular factors support virus-host interactions

Both cellular and viral proteins can undergo phase separation and form membraneless compartments that concentrate biomolecules. The p26 movement protein from single-stranded, positive-sense Pea enation mosaic virus 2 (PEMV2) separates into a dense phase in nucleoli where p26 and related orthologues must interact with fibrillarin (Fib2) as a pre-requisite for systemic virus movement. Using in vitro assays, viral ribonucleoprotein complexes containing p26, Fib2, and PEMV2 genomic RNAs formed droplets that may provide the basis for self-assembly in planta. Mutating basic p26 residues (R/K-G) blocked droplet formation and partitioning into Fib2 droplets or the nucleolus and prevented systemic movement of a Tobacco mosaic virus (TMV) vector in Nicotiana benthamiana. Mutating acidic residues (D/E-G) reduced droplet formation in vitro, increased nucleolar retention 6.5-fold, and prevented systemic movement of TMV, thus demonstrating that p26 requires electrostatic interactions for droplet formation and charged residues are critical for nucleolar trafficking and virus movement. p26 readily partitioned into stress granules (SGs), which are membraneless compartments that assemble by clustering of the RNA binding protein G3BP following stress. G3BP is upregulated during PEMV2 infection and over-expression of G3BP restricted PEMV2 RNA accumulation >20-fold. Deletion of the NTF2 domain that is required for G3BP condensation restored PEMV2 RNA accumulation >4-fold, demonstrating that phase separation enhances G3BP antiviral activity. These results indicate that p26 partitions into membraneless compartments with either proviral (Fib2) or antiviral (G3BP) factors.

CircRNAs and their regulatory roles in cancers

Circular RNAs (circRNAs), a novel type of non-coding RNAs (ncRNAs), have a covalently closed circular structure resulting from pre-mRNA back splicing via spliceosome and ribozymes. They can be classified differently in accordance with different criteria. As circRNAs are abundant, conserved, and stable, they can be used as diagnostic markers in various diseases and targets to develop new therapies. There are various functions of circRNAs, including sponge for miR/proteins, role of scaffolds, templates for translation, and regulators of mRNA translation and stability. Without m7G cap and poly-A tail, circRNAs can still be degraded in several ways, including RNase L, Ago-dependent, and Ago-independent degradation. Increasing evidence indicates that circRNAs can be modified by N-6 methylation (m6A) in many aspects such as biogenesis, nuclear export, translation, and degradation. In addition, they have been proved to play a regulatory role in the progression of various cancers. Recently, methods of detecting circRNAs with high sensitivity and specificity have also been reported. This review presents a detailed overview of circRNAs regarding biogenesis, biomarker, functions, degradation, and dynamic modification as well as their regulatory roles in various cancers. It’s particularly summarized in detail in the biogenesis of circRNAs, regulation of circRNAs by m6A modification and mechanisms by which circRNAs affect tumor progression respectively. Moreover, existing circRNA detection methods and their characteristics are also mentioned.

Assembly of multicomponent machines in RNA metabolism: A common theme in mRNA decay pathways

Multicomponent protein-RNA complexes comprising a ribonuclease and partner RNA helicase facilitate the turnover of mRNA in all domains of life. While these higher-order complexes provide an effective means of physically and functionally coupling the processes of RNA remodeling and decay, most ribonucleases and RNA helicases do not exhibit sequence specificity in RNA binding. This raises the question as to how these assemblies select substrates for processing and how the activities are orchestrated at the precise moment to ensure efficient decay. The answers to these apparent puzzles lie in the auxiliary components of the assemblies that might relay decay-triggering signals. Given their function within the assemblies, these components may be viewed as "sensors." The functions and mechanisms of action of the sensor components in various degradation complexes in bacteria and eukaryotes are highlighted here to discuss their roles in RNA decay processes. This article is categorized under: RNA Turnover and Surveillance > Regulation of RNA Stability RNA Turnover and Surveillance > Turnover/Surveillance Mechanisms RNA Interactions with Proteins and Other Molecules > Protein-RNA Recognition.

MiR-92b-3p Inhibits Proliferation of HER2-Positive Breast Cancer Cell by Targeting circCDYL

Objectives

Circular RNA (circRNA) is a novel class of RNA, which exhibits powerful biological function in regulating cellular fate of various tumors. Previously, we had demonstrated that over-expression of circRNA circCDYL promoted progression of HER2-negative (HER2^–) breast cancer via miR-1275-ULK1/ATG7-autophagic axis. However, the role of circCDYL in HER2-positive (HER2⁺) breast cancer, in particular its role in modulating cell proliferation, one of the most important characteristics of cellular fate, is unclear.

Materials and methods

qRT-PCR and in situ hybridization analyses were performed to examine the expression of circCDYL and miR-92b-3p in breast cancer tissues or cell lines. The biological function of circCDYL and miR-92b-3p were assessed by plate colony formation and cell viability assays and orthotopic animal models. In mechanistic study, circRNAs pull-down, RNA immunoprecipitation, dual luciferase report, western blot, immunohistochemical and immunofluorescence staining assays were performed.

Results

CircCDYL was high-expressed in HER2⁺ breast cancer tissue, similar with that in HER2^– breast cancer tissue. Silencing HER2 gene had no effect on expression of circCDYL in HER2⁺ breast cancer cells. Over-expression of circCDYL promoted proliferation of HER2⁺ breast cancer cells but not through miR-1275-ULK1/ATG7-autophagic axis. CircRNA pull down and miRNA deep-sequencing demonstrated the binding of miR-92b-3p and circCDYL. Interestingly, circCDYL did not act as miR-92b-3p sponge, but was degraded in miR-92b-3p-dependent silencing manner. Clinically, expression of circCDYL and miR-92b-3p was associated with clinical outcome of HER2⁺ breast cancer patients.

Conclusion

MiR-92b-3p-dependent cleavage of circCDYL was an essential mechanism in regulating cell proliferation of HER2⁺ breast cancer cells. CircCDYL was proved to be a potential therapeutic target for HER2⁺ breast cancer, and both circCDYL and miR-92b-3p might be potential biomarkers in predicting clinical outcome of HER2⁺ breast cancer patients.

Circular RNAs Interaction with MiRNAs: Emerging Roles in Breast Cancer

Despite significant advances in cancer therapy strategies, breast cancer is one of the most common and lethal malignancies worldwide. Characterization of a new class of RNAs using next-generation sequencing opened new doors toward uncovering etiopathogenesis mechanisms of breast cancer as well as prognostic and diagnostic biomarkers. Circular RNAs (circRNAs) are a novel class of RNA with covalently closed and highly stable structures generated primarily from the back-splicing of precursor mRNAs. Although circRNAs exert their function through various mechanisms, acting as a sponge for miRNAs is their primary mechanism of function. Furthermore, growing evidence has shown that aberrant expression of circRNAs is involved in the various hallmarks of cancers. This paper reviews the biogenesis, characteristics, and mechanism of functions of circRNAs and their deregulation in various cancers. Finally, we focused on the circRNAs roles as a sponge for miRNAs in the development, metastasis, angiogenesis, drug resistance, apoptosis, and immune responses of breast cancer.

The Regulation Network and Clinical Significance of Circular RNAs in Breast Cancer

Breast cancer is one of the most common malignant tumors in women worldwide. Circular RNA (circRNA) is a class of structurally stable non-coding RNA with a covalently closed circular structure. In recent years, with the development of high-throughput RNA sequencing, many circRNAs have been discovered and have proven to be clinically significant in the development and progression of breast cancer. Importantly, several regulators of circRNA biogenesis have been discovered. Here, we systematically summarize recent progress regarding the network of regulation governing the biogenesis, degradation, and distribution of circRNAs, and we comprehensively analyze the functions, mechanisms, and clinical significance of circRNA in breast cancer.

Cancer cell adaptability: turning ribonucleoprotein granules into targets

Stress granules (SGs) and processing bodies (P-bodies) are membraneless cytoplasmic condensates of ribonucleoproteins (RNPs). They both regulate RNA fate under physiological and pathological conditions, and are thereby involved in the regulation and maintenance of cellular integrity. During tumorigenesis, cancer cells use these granules to thrive, to adapt to the harsh conditions of the tumor microenvironment (TME), and to protect themselves from anticancer treatments. This ability to provide multiple outcomes not only makes RNP granules promising targets for cancer therapy but also emphasizes the need for more knowledge about the biology of these granules to achieve clinical use. In this review we focus on the role of RNP granules in cancer, and on how their composition and regulation might be used to elaborate therapeutic strategies.

Defining the landscape of circRNAs in non-small cell lung cancer and their potential as liquid biopsy biomarkers: a complete review including current methods

Despite the significant decrease in population-level mortality of lung cancer patients as reflected in the Surveillance Epidemiology and End Results program national database, lung cancer, with non-small cell lung cancer (NSCLC) in the lead, continues to be the most commonly diagnosed cancer and foremost cause of cancer-related death worldwide, primarily due to late-stage diagnosis and ineffective treatment regimens. Although innovative single therapies and their combinations are constantly being tested in clinical trials, the five-year survival rate of late-stage lung cancer remains only 5% (Cancer Research, UK). Henceforth, investigation in the early diagnosis of lung cancer and prediction of treatment response is critical for improving the overall survival of these patients. Circular RNAs (circRNAs) are a re-discovered type of RNAs featuring stable structure and high tissue-specific expression. Evidence has revealed that aberrant circRNA expression plays an important role in carcinogenesis and tumor progression. Further investigation is warranted to assess the value of EV- and platelet-derived circRNAs as liquid biopsy-based readouts for lung cancer detection. This review discusses the origin and biology of circRNAs, and analyzes their present landscape in NSCLC, focusing on liquid biopsies to illustrate the different methodological trends currently available in research. The possible limitations that could be holding back the clinical implementation of circRNAs are also analyzed.

Circular RNAs: Expression, localization, and therapeutic potentials

Circular RNAs (circRNAs) are RNAs with a unique circular structure that is generated from back-splicing processes. These circular molecules were discovered more than 40 years ago but failed to raise scientific interest until lately. Increasing studies have found that these circular RNAs might not just be byproducts of the splicing process but possess important regulatory functions through different cellular events. Most circular RNAs are currently being studied in the field of cancer, and many of them have been confirmed to be involved in the process of tumorigenesis. However, many circular RNAs are implicated in the developmental stages of diseases other than cancer. In this review, we focus on discussing the role of circular RNAs in non-cancer diseases, especially in cardiovascular diseases. Following the summary of the life cycle of circRNAs, we provide input on studying circRNA-protein interactions based on our experience, which modulate protein translocation. Furthermore, we outline the potential of circRNAs to be potent biomarkers, effective therapeutic targets, and potential treatments in cardiovascular diseases as well as other non-cancer fields.

The multi-functional RNA-binding protein G3BP1 and its potential implication in neurodegenerative disease

Ras-GTPase-activating protein (GAP)-binding protein 1 (G3BP1) is a multi-functional protein that is best known for its role in the assembly and dynamics of stress granules. Recent studies have highlighted that G3BP1 also has other functions related to RNA metabolism. In the context of disease, G3BP1 has been therapeutically targeted in cancers because its over-expression is correlated with proliferation of cancerous cells and metastasis. However, evidence suggests that G3BP1 is essential for neuronal development and possibly neuronal maintenance. In this review, we will examine the many functions that are carried out by G3BP1 in the context of neurons and speculate how these functions are critical to the progression of neurodegenerative diseases. Additionally, we will highlight the similarities and differences between G3BP1 and the closely related protein G3BP2, which is frequently overlooked. Although G3BP1 and G3BP2 have both been deemed important for stress granule assembly, their roles may differ in other cellular pathways, some of which are specific to the CNS, and presents an opportunity for further exploration.

Methods to study circRNA-protein interactions

Circular RNAs (circRNAs) have been studied extensively in the last few years, uncovering functional roles in a diverse range of cell types and organisms. As shown for a few cases, these functions may be mediated by trans-acting factors, in particular RNA-binding proteins (RBPs). However, the specific interaction partners for most circRNAs remain unknown. This is mainly due to technical difficulties in their identification and in differentiating between interactors of circRNAs and their linear counterparts. Here we review the currently used methodology to systematically study circRNA-protein complexes (circRNPs), focusing either on a specific RNA or protein, both on the gene-specific or global level, and discuss advantages and challenges of the available approaches.

A narrative review of circular RNAs as potential biomarkers and therapeutic targets for cardiovascular diseases

Circular RNAs (circRNAs), a novel class of non-coding RNA, are produced by back-splicing and were initially considered to be by-products of splicing. In recent years, computational technology and experimental evidence have revealed the tremendous amounts and potential physiological or pathological functions of this novel non-coding RNA species. At present, the roles of circRNAs in neurological diseases, immune diseases, and cancers have come to light. In addition, increasing studies have identified the expression profiles of circRNA in cardiovascular diseases (CVDs) and revealed the involvement of circRNAs in the pathogenesis of CVDs which are the leading cause of mortality and morbidity worldwide, and result in substantial health and financial burden. Despite current improvements in diagnostic and therapeutic approaches, survival and prognosis of CVDs patients remain relatively poor. Due to the involvements of circRNAs in CVDs and their outstanding characteristics of high stability, conservation, and tissue- or developmental-specificity, circRNA-based biomarkers or gene therapy may be effective approaches to reduce CVDs burden. In the review, we systematically summarized the formation mechanisms, functional models, and research approaches of circRNAs, and several circRNAs involved in CVDs. Finally, we proposed that developing circRNAs as biomarkers or circRNA-based therapeutic strategies based on biological or physical materials may be promising to diagnose or treat CVDs in the future.